1. Field of the Invention
The present invention generally relates to patterned recording media and a method of manufacturing the same, and more specifically, to patterned recording media and a method of manufacturing the same using selective thermal coupling.
2. Description of the Related Art
In conventional magnetic recording systems a written bit size is defined by the dimensions of the recording head. A written domain comprises several hundred magnetic grains. For example, for the highest recording density products being introduced in the market today (20 Gb/in2), the bit cell is about 620 nmxc3x9752 nm. To support such areal densities the microstructure of the recording media has been engineered to consist of non-exchange coupled grains with grain diameters of about 10 nm. Therefore, a recorded domain involves about 400 grains.
Therefore, one approach to achieving higher recording densities is to reduce the bit size and consequently the media grain size. However, this approach is limited because at a critical grain volume, the magnetic grains become thermally unstable and spontaneously switch magnetization direction at normal operating temperatures due to superparamagnetism and are unable to maintain the magnetization orientation imposed on them during the writing process. In addition, as the number of grains is reduced, the noise arising from statistical fluctuations in grain positions or orientation increase.
Another approach to increasing recording density is to modify the microstructure of the media so that a bit is stored in a single grain, or a multiplicity of grains or magnetic clusters which are fully exchange coupled within the recorded bit dimensions. This approach commonly referred to as xe2x80x9cmagnetic media patterningxe2x80x9d requires that adjacent grains or clusters be magnetically isolated. This approach is perceived as a necessary means for extending magnetic recording to meet storage densities in excess of 100 Gb/in2.
Conventional methods of patterning magnetic media encompass a wide variety of techniques ranging from conventional lithography, to the use of particle and photon sources in combination with masks to produce patterned structures. For example, U.S. Pat. No. 6,168,845 to Fontana et al. (hereinafter xe2x80x9cFontanaxe2x80x9d) discloses a method of making patterned magnetic media using selective oxidation. The Fontana method includes depositing a layer of magnetic material on a substrate (e.g. a conventional nickel-phosphorus plated aluminum-magnesium substrate), covering portions of the magnetic layer with a protective mask that determines the patterning of the non-magnetic zones, and exposing the protective mask and the uncovered portions of the magnetic layer to an oxygen plasma. The oxygen plasma oxidizes the magnetic layer so that the uncovered portions have a reduced local magnetic moment. The result is a patterned magnetic medium with discrete magnetic and non-magnetic zones.
The utilization of ion beam implantation to achieve patterned media, has been disclosed in xe2x80x9cMethod for Spatially Modulating Magnetic Properties Using Ion Beam Implantationxe2x80x9d, J. Baglin, E. E. Marinero and K. Rubin, (AM9-98-096).
Such conventional methods aim to significantly alter the magnetic properties of the regions exposed to the particles, energy sources, ions or reactive species. The areas of the magnetic material which were prevented from exposure by the mask, exhibit different magnetic properties from the exposed areas and information can be recorded and retrieved by taking advantages of the differences in magnetic properties between these two different material regions.
However, these methods have several drawbacks that inhibit their use in magnetic media manufacturing applications. For example, a storage density of over 100 Gb/in2 would require an exposure mask having a feature size of about 40 nm over large areas. In addition, the mask must be accurately aligned and positioned. Further, in the case of particle implantation and reactive ion etching, the mask may have a short lifetime because the impinging species are expected to be heated and deposited on the non-transmissive areas of the mask. In short, these methods generally require additional hardware and/or processing steps which result in higher fabrication costs and longer manufacturing cycle times.
In view of the foregoing problems of the conventional techniques, an object of the present invention is to provide a structure and method for patterning recording media.
The inventive method includes selectively thermally coupling a recording medium and a heat source to alter a chemical composition of the recording medium. The chemical composition may be altered according to a predetermined pattern, such as concentric circles or parallel tracks.
Further, altering the chemical composition may causes an altered magnetic order of the recording medium, an altered dielectric constant of the recording medium, an altered electrical conductivity of said recording medium, or an altered thermal conductivity of said recording medium. Further, altering the dielectric constant may cause an altered reflectivity of the recording medium. In addition, altering an electrical conductivity may cause an altered electron transport property of the recording medium.
Further, selectively thermally coupling may include selectively directing an incident thermal wave to the recording medium to form a direct thermal coupling between the heat source and the recording medium.
The inventive method may also include depositing the recording medium on a substrate. Further, the medium may include cobalt and chromium, and the substrate may include glass, silicon, quartz, sapphire, AlMg or a ceramic substrate. More specifically, the medium may include CoxCr1-x, where x is in a range from 0.63 to 0.75.
In addition, the heat source may include a near-field thermal probe or a nanoheater. The heat source may or may not physically contact the recording medium.
More specifically, the chemical composition may be altered by one of interfacial mixing, interfacial reactions selective oxidation, structural relaxation, phase segregation and phase change. In addition, altering the chemical composition may transform the medium from a paramagnetic medium to a ferromagnetic medium, or it may transform the medium from a ferromagnetic medium to a paramagnetic medium.
Further, altering the chemical composition may alter a magnetic axis orientation of the medium or it may reduce magnetization or coercivity of the medium. Furthermore, selectively thermally coupling may include selective near-field radiative coupling of blackbody radiation from the heat source to the recording medium. In addition, thermal energy may be transferred to the medium by conductive heating or by radiative heating.
The present invention also includes an inventive apparatus for patterning a recording medium. The inventive apparatus includes a heat source for generating and directing an incident thermal wave to a recording medium, the thermal wave altering a chemical composition of a recording medium, and a controller for coordinating a mutual position of the incident thermal wave and the recording medium so as to thermally couple the heat source and the recording medium.
Further, the heat source may include, for example, a nanoheater, a near field thermal probe or an atomic force thermal probe. In addition, the heat source may include a heating plate for developing a thermal energy which couples the heat source to the recording medium, and a heat sink connected to the heating plate. The heating plate may include, for example, a tip for concentrating, and directing a thermal energy.
The heat source may be heated, for example, by a resistive heating element thermally coupled to the heat sink. Alternatively, the heat source in the inventive apparatus may be heated by using an optical waveguide coupled to the heat sink, for carrying a focused laser beam. The optical waveguide may include, for example, an optical fiber. The optical waveguide may be, for example, a planar optical waveguide.
An especially efficient embodiment of the present invention includes an inventive read/write head assembly, which includes a read/write head, a heat source connected to the read/write head for generating and directing an incident thermal wave to a recording medium, the thermal wave altering a chemical composition of a recording medium, and a controller for coordinating a mutual position of the incident thermal wave and the recording medium so as to thermally couple the heat source and the recording medium. For example, the chemical composition may be altered according to a predetermined pattern, and the heat source may pattern the recording medium during a read/write operation of the read/write head assembly.
The present invention also includes an inventive patterned recording medium which includes a substrate and a single layer medium formed on the substrate having a portion which has been patterned by altering a chemical composition of the medium using selective thermal coupling.
Furthermore, the present invention includes a method for manufacturing a patterned magnetic disk which includes depositing a recording medium on a substrate, selectively thermally coupling the recording medium and a heat source so as to alter a chemical composition of the recording medium and depositing a protective coating on the recording medium.
Thus with the unique and unobvious features of the invention, a simple, versatile method for manufacturing patterned recording media is provided which requires no lithographic masks or additional processing steps. Further, the inventive patterned recording medium is thin and substantially smooth to better facilitate a read/write operation, and an apparatus for patterning recording medium is simple and inexpensive and may be incorporated into a conventional read/write assembly with little alteration of the read/write assembly.